Encyonopsis neerlandica, Vijver & Verweij & Wal & Mertens, 2012

Vijver, Bart Van De, Verweij, Geurt L., Wal, Jako Van Der & Mertens, Adrienne, 2012, Encyonopsis neerlandica, a new freshwater diatom species (Bacillariophyta) from moorland pools in The Netherlands, Phytotaxa 66 (1), pp. 43-48 : 44-46

Encyonopsis neerlandica sp.nov. ( Figs 1–23)

Valvae leviter (speciminibus minoribus) ad moderate (speciminibus maioribus) dorsiventrales, clare ad anguste lanceolatae (numquam lineares) margine dorsali convexi margineque ventrali leviter convexi. Apices protractae, acute rotundatae, rostratae ad leviter capitatae. Longitudo 15–26 µm, latitudo 3.5–4.5 µm. Sternum angustissimum, lineare, area centralis nulla. Raphe filiformis, paulo curvata ad marginibus ventralibus, terminis proximalibus ad latus dorsale inclinatis. Terminationes proximales formantes pori inconspicui. Fissurae distales deflexae, non uncinatae vel flexae. Striae leviter radiatae ad moderate radiatae in apices, aequidistantes omnino, 24–28 in 10 µm.

LM Morphology ( Figs 1–17): —Valves weakly (smaller specimens) to moderately (larger specimens) dorsiventral, narrowly lanceolate (never linear) with convex dorsal margin and slightly convex ventral margin. Apices protracted, acutely rounded, rostrate to subcapitate. Valve dimensions (n = 25): length 15–26 µm, width 3.5–4.5 µm, valve length/width ratio 4.2–6.3. Sternum very narrow, linear. Central area absent, striae rarely occur in central area, more distantly spaced. Raphe filiform, curved to the ventral side but with dorsally deflected central raphe endings terminating in inconspicuous central pores. Transapical striae weakly radiate to moderately radiate near the apices, almost equally spaced throughout the entire valve, dorsally 25–28, ventrally 24–26 in 10 µm although in some cases up to 30 striae can be found near the apices. Areolae not discernible in LM.

SEM MORPHOLOGY ( Figs 18–23): —Striae composed of 5–6 small areolae, 40–45 in 10 µm ( Fig. 19). Areolae rounded near the valve margins, becoming slightly transapically elongated near the axial area ( Figs 19, 20), except near the central area where areolae on the dorsal side bordering the axial area are rounded. Striae continuing without interruption on the mantle, forming series of 3–4 rounded areolae, the last one being slit-like ( Fig. 18, see arrows). Raphe curved to the ventral side ( Fig. 18) but at 1/3 from the valve apices, a sudden shift in direction is visible, becoming dorsally deflected to almost straight with slightly enlarged, deflected proximal endings ( Fig. 19). Distal raphe fissures deflected, not hooked or bent to the ventral side ( Fig. 20), terminating on the valve face in a pore. Internally striae forming rather wide grooves with undulating margins ( Figs 21, 22, 23). Areolae appearing as small rounded pores, separated from each other by slightly raised silica struts ( Fig. 22). Proximal raphe endings short, weakly deflected ( Fig. 22). Central nodule weakly raised, eroded in all observed valves ( Fig. 22). Distal raphe endings terminating as well developed helictoglossae ( Fig. 23).

Type: — Galgenmatenven, Ambt Delden, Twente (province of Overijssel), The Netherlands, sample D1010-41 (52°15'23.35"N, 6°40'20.70"O), leg. G. Verweij, coll. date 27/05/2010, slide no. BR-4270 (holotype BR, slide PLP-214 (isotype University of Antwerp , Belgium), slide ZU8/49 (isotype BRM).

Etymology: —The specific epithet neerlandica refers to the country where the species was found: The Netherlands.

Habitat: — Encyonopsis neerlandica is described from a weakly buffered isolated moorland pool in the eastern part of the Netherlands. The pool is characterized by a weakly acid to weakly alkaline pH (6.4–7.6) and a moderate specific conductance value (150–340 µS/cm). Based on the measured nutrients, the pool can be classified as mesotrophic and oligo- to β- mesosaprobic. A second large population was found in the Klotven near the Dutch-Belgian border with similar ecological conditions. A reanalysis of moorland pool samples where Encyonopsis valves were found in the past showed that Encyonopsis neerlandica is widespread, with observations from several provinces in the Netherlands (Noord-Brabant, Drenthe, Friesland, Overijssel). Most of these moorland pools were rather oligotrophic, weakly acid and oxygen-rich. The accompanying diatom flora included Brachysira procera Lange-Bert & Gerd Moser (1994: 55) , Brachysira neoexili s Lange-Bert. in Lange-Bertalot & Gerd Moser (1994: 51), Stauroforma exiguiformis (Lange-Bert. 1993: 45) Flower, Jones & F.E. Round (1996: 53) and several species of Eunotia .